1. Field of the Invention
The present invention relates generally to a wearable tactile sensory aid for deaf persons, and more particularly pertains to a portable tactile sensory aid designed to be worn by profoundly or totally deaf individuals which provides them with information on voice fundamental frequency which is simultaneously encoded to provide both frequency of actuation and spatial indications thereof.
2. Discussion of the Prior Art
The prior art provides an extensive history on tactile sensory aids for the deaf. When wearable, such devices have typically been implemented as single channel devices. In general, these sensory aids are designed to provide deaf persons with access, via the sense of touch, to the acoustic waveform of speech.
Intonation patterns, i.e., the patterns of variation in the fundamental frequency of the voice over time, play several roles in speech. For example, they help define where sentences begin and end, they mark the more important words in a sentence, and they sometimes serve to differentiate questions from statements. The expected benefits of a wearable tactile intonation display to a deaf individual are faster and more accurate lipreading and improvements in the quality and intelligibility of self-generated speech. Although intonation information is not accessible by lipreading, many deaf persons have sufficient residual hearing for the perception of intonation when using hearing aids. The present invention is not generally intended for those partially deaf persons, but for those deaf persons whose hearing is so badly damaged that hearing aids are either useless, or, at best, provide access only to patterns of variation in amplitude over time.
There is a long history in the prior art of attempts to alleviate the problems of deafness by converting the sounds, movements, or airflow characteristics of speech into patterns that can be perceived via the undamaged senses of vision or touch. Regarding the tactile representation of intonation patterns, the simplest way to convey acoustical information through the sense of touch is to amplify the speech waveform and feed it to a single electromechanical transducer that is in contact with the skin. A single channel device of this type was first described in the prior art in the 1920s. A more modern version of this early single channel is presently commercially available as the Siemens Monofonator, which is a desk-top unit.
Wearable single channel devices that employ mechanical transduction of the acoustic waveform have also been described in the prior art. In addition, it has been pointed out that for the totally deaf individual, a high power hearing aid can serve, in effect, as a wearable, single channel, tactile stimulator.
Experiments on the psychophysics of the sense of touch have shown that there should be sufficient frequency discrimination to provide at least partial access to intonation patterns. Evaluation of the single channel tactile devices mentioned above, however, has failed to provide evidence that they serve to provide information on intonation. Instead, their benefits appear to be limited to perception of the amplitude envelope of the speech signal.
It is possible to provide information on intonation in a single channel display by suitable forms of signal processing. However an alternative approach also exists in representing fundamental frequency as a position of vibratory stimulation using an array of transducers. The changes of frequency that constitute intonation then become encoded as movements of tactile sensation, thereby acquiring considerable perceptual salience. A display of this type using only the encoded position within an array was developed in the early 1970s and was used in a promising evaluative study with deaf children. However, this was a desk-top unit, and could only be used for brief periods of one-to-one instruction.